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What is the impact of copper paving on EMI?

2019-07-30 11:42:16
Theory and analysis of paving of double-panel PCB system
1. Good aspects of paving:
Pay attention to the trace of the edge of the PCB of the signal line. If the ground is used, the external signal coupling of this signal line is reduced; the PCB is grounded at the edge of the PCB;
Copper is laid between the signal lines, which reduces crosstalk between signals. The EMI radiation in crosstalk is indirectly related to it!
If both can achieve or achieve EMI effect will be good! The paving is not the number of places to be counted by area. It is necessary to have a target to lay the ground to have a good effect!

2. My point of view:
The PCB has copper-clad conditions, and this copper plating is useful. If it can improve the performance of EMI, it is recommended to use the rule of PCB copper.
3. Note:
In this design, it is necessary to ensure that the ground plane of the signal and the impedance of the reference ground potential of the system are small enough; otherwise, the paving will have an impact on radiation interference or radiation interference!
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Actual case sharing
For high-frequency application electronic product lines; due to the common mode current interference EMI problem, we need to increase the common mode inductance and its combination of LCM*C at the DC-DC DC current output terminal and the interface connector end of the functional circuit. The design of the EMI filter; at this time, the PCB layout and layout will affect our high frequency EMI; the analysis is as follows:

1. When there is a filter design of the common mode inductor in the electronic circuit, the PCB of the TOP layer and the PCB floor of the BOTTOM bottom layer will have the coupling capacitor Cp when the PCB is designed in the front and rear stages; the high frequency disturbance signal will be The coupling impedance affects the noise impedance performance of the common mode inductor; the equivalent circuit is as follows:

2. For example, the design of the system LCM device has a stray capacitance of 2pF; its resonant frequency is around 4MHZ; the design of the copper-plated ground of the PCB, due to the wiring of the PCB, the input trace and the copper-plated ground of the PCB bring 6pF Coupling capacitance parameters; after its LCM resonance point will reduce its impedance value - the frequency & impedance characteristic curve reference data shown above; in the EMI test will bring high frequency EMI problem of high frequency > 4MHZ!
3. When designing PCB double-panel wiring copper ground; improving PCB layout and routing in some circuit designs can reduce high-frequency EMI electromagnetic interference; simple optimized PCB design reference is as follows:

Note: If there is a noise coupling source in the ground plane, the ground plane should not be close to the sensitive input circuit.